Tuning devices



5 Sheets-Sheet 1 Sept. 4, 1956 J. w. QUITMEYER TUNING DEVICES Filed May'7, 1952 Sept. 4, 1956 J. w. QUITMEYER 2,761,994

' TUNING DEVICES Filed May 7, 1952 5 Sheds-Sheet 2 T I I TIM;

TUNING DEVICES s sheets sheef 3 Filed. May 7. 2

03 Mfr [a Z ,7 M l a I I Sept. 4, 1956 J, w. QUITMEYER TUNING DEVICES 5Sheets-Sheet 5 Filed May 7, 1952 MU M H g/ZZ w pizii INVENTOR. fig??-auiimeyex' I17TOY/V5'/$ United States Patent TUNING'DEVICES John W.Quitmeyer, Rochester, Mich. Application May 7, 1952,Serial No. 286,48012 Claims. (Cl. 31-5-76) This invention relates generally to tuningdevices which are particularly adapted, among other uses, for tuningmusical instruments playingthe chromatic tempered scale of notes.

An object of this invention is'to provide an improved device of thecharacter described.

Another object of this invention is to provide such a device which isreadily transportable and usable by a musical instrument service mansuch as a piano tuner.

Another object of this invention is to'provide such a device in whichthe usual piano tuning tools may be carried in the same container. I

Another object of this invention is to provide such a device which maybe placed in a desired location on a piano during the tuning operationand which will provide light for iluminating the works ofthe-prano and asignal which will indicate when'the struck note ofthe piano is in tune.

Another object of this invention is to provide such a device in which,when a note is beingstruck, the intermittently illuminated lamp willilluminate the stroboscoprc disk at the frequency of the played noteandwill illunnnate the disk at a high frequency when no note is beingplayed.

Another object is to provide such a device in WhlCh asound-to-electrical converting pick-up device such as a microphonereceives the sound from the played note to normally control thefrequency of. illumination of the light source and in which feed backmeans'controls the illumination of the stroboscopic diskwhen thestrength of the received sound Wave is below a predetermined minimumvalue.

Another object of this invention is to provide a stroboscopic disk whichmay be rotated .at constant speed and which will indicate the correcttuning of any note in any octave of the chromatic tempered scaleofnotes,

Another object is to provide such a disk in which the pattern will bevaried, depending upon the octave in which the struck chromatic temperednote occurs.

Another object of thisinvention isto'provide suitable indicia means forindicating which of the rows of rotating indicia marks correspond to thevarious chromatic notes when played by instruments in various keys.

Other objects of this invention will be apparent from the specification,the appended claims and the drawings, in which drawings:

Figure 1 is a perspective view, with-certain ofthe parts broken away,showing the form the invention takes when it is being transported;

Fig. 2 is a side elevational view of the portion of the apparatus shownin Fig. '1 with the cover removed;

Fig. 3 is a view taken substantially along the line 3--3 of Fig. 2 andlooking in the direction of the arrows;

Fig. 4 is a view taken substantially along the line 44 of Fig. 3 andlooking in the direction of the arrows;

Fig. 5 is a view taken substantially along the line 5-5 of Fig. 2 andlooking in the direction of the arrows;

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Fig. 6 is a view taken substantially along the line 66 of Fig. 3 andlooking in the direction of the arrows;

Fig. 7 is a view taken substantially along the line 77 of Fig. 3 andlooking in the direction of the arrows;

Fig. 8 is a View taken substantially along the line 88 of Fig. 7 andlooking in the direction of the arrows;

Fig. 9 is a view showing one of the indexing members for determiningwhich row corresponds to which note of the chromatic scale;

Fig. 10 is a detail of the second member which cooperates with themember of 'Fig. 9;

Fig. 11 is a detailed view of the rotatable member showing the type ofindiciamarks utilized and the way in which any unevenness in-the numberof marks is compensated for;

Figs. 12, 13 and 14 are detailed views showing the patterns formed bythe indicia as the same note is played in three diiferent octaves; and,

Fig. 15 is a schematic view of the circuit diagram for controlling thelight source.

Different types of stroboscopic apparatus have previously been suggestedfor use by tuners of musical instruments for accurately determining whenthe instrument is in tune. These instruments'have not come into generaluse by piano tuners who must, of necessity, go from house to house,because they-have been such that they could not be easily transported.

Referring to the drawings by characters of reference, the numeral 1indicates generally a stroboscopic type of piano tuning devicecomprising a first housing portion 2 and a second housing portion 4which cooperate together to provide a compact, not easily damaged,portable stroboscopic piano tuning instrument. The portion 4 isremovable from the portion 2 as shown by its position shown in dot dashline of Fig. l. The portion 4,contains a tool compartment 6 in whichmaybe carried the usual piano tuning tools. A hinged cover 8-is providedfor the compartment 6. The lower housing portion 2 is providedexternally with screw eyes 12 to which maybe hooked a carrying strap 14which serves as a handle for transporting the device 1.

The first housing portion '2'has end walls 16 and 18, a bottom wall 20,a top wall 22, a rear wall 24, and a removable front wall or panel 26 towhich panel the internal Working parts for the housing portion 2 aresecured. The Walls 16, 18,20 and 22 are providedwith an internalshoulder 28 against which the removable front 26 seats. The wall 26 isprovided with a viewing aperture 30 which may be closed-with atransparentshield 32 to prevent entrance of foreign material into theinterior cavity 34.

The electrical network 36 schematically shown in Fig. 15 is carried by asheet metal chassis 38 which is suitably and rigidly attached to theremovable wall 26. The chassis 38 shields the circuit Wires of thenetwork 36 from the radiation produced by the ionization of a suitablegas, such as neon, located within a U-shaped glass tube 40 carried onthe inside surface of the removable wall 26. The tube 40 extendsaroundgthree sides of the substantially rectangular aperture 30. Thechassis 38 carries tube sockets 42 opening throughthe'upper surfacethereof for receiving the vacuum tubes'or valves 44, 46, 48 and 5t) andfor receiving the full wave rectifier valve 52 which supplies the directcurrentvoltage'between the positive bus 54 and the negative'bus 56 (Fig."15).

The circuit wires forming the network shown in Fig. 15 externally of thechassis 38 are shielded by means of shielded cables of theusual type inwhich the external,

shielding conductor 58, is grounded and completely shields the innerconductor except for a short length 60 extending from the microphonepick-up device 62 to the control grid of the valve '44 which unshielded,portion picks up radiation from the ionized neon gas in the tube 44. Thechassis 38 is provided with a central aperture 64 which permits aportion of the rotatable hollow cylinder or drum 66 to extend within itsinterior to permit a compact assembly. The cylinder 66 is provided withinternal webs or supports 68 and 70 which are spaced axially thereof asshown in Fig. 3.

The support 70, shown in detail in Figs. 7 and 8, is provided with fanblades 72 and apertures 74 and the support 68 with apertures 76 tocirculate air for sgh the interior of the drum and over the tubes M-32wt c it is being rotated. The supports are provided with alignedapertures at the axial center of the drum 66 for snugly receiving anaxle shaft 78 which is supported at one end in a self-oiling bearingcarried by a support mounted on the upper surface of the chassis 38 andat its other end by the shaft of a synchronous electric motor generallydesignated 82 and which may be of the type used for driving electricclocks. The motor 82 is mounted on the chassis 38 and rotates the drumone revolution per second.

The energization of the motor 82 is controlled by means of a usualswitch not shown carried within the chassis 38 and controlled by a knob84 on the front face of the removable panel 26. This switch alsocontrols in a suitable manner not shown the energization of the network36 so that the motor 82 and the network 36 are energized concurrently.

The front vertical wall 86 of the chassis 38 is provided with aforwardly, outwardly extending portion which is suitably secured as bythe bolts 90 to the inner surface of the removable wall 26 to define anopen ended chamber 92 adjacent the bottom wall 20. The bottom wall 28adjacent the chamber 92 is provided with an aperture 94 which may beclosed, if desired, as by means of a transparent panel 96. A socket 98is supported by the u casing wall 86 by a bolt 100 for positioning alight bulb 102 below the wall portion 88 and above the aperture 94.Light radiating from the bulb 102 passes through the aperture 94 so thatwhen the device 1 is placed on top of a piano, fragmentarily shown at194, it will light its interior works. Preferably the wall 24) isprovided with a plurality of rubber supports 166 to prevent anyscratching of the piano by the device 1 when it is being rested thereon.The wall portion 88 prevents the light from the bulb 102 fromilluminating the drum 66. A control knob 103 is provided to control aswitch 105 controlling the bulb 102.

The microphone pick-up 62 is supported on the front wall 86 of thecasing 36 by a bolt 108 which has one end rigidly secured to the wall 86and its other end clamping an encircling band 110 about the microphone62. The microphone 62 has its sensitive surface facing downwardly forreceiving sound energy through an aperture 112 in the bottom wall 20.The aperture 112 may be closed by suitable sound transmitting screen 114to prevent foreign objects from directly touching the microphone 62.

The outer surface of the drum 66 is provided with 13 rows ofwedge-shaped indicia marks 116, 118, 12%, 122, 124, 126, 128, 130, 132,134, 136, 138 and 140. The rows of indicia 116 and 140 are similar andrepresent the same chromatic note except that there are twice as manymarks in the row 140 as in the row 116.

In the chromatic scale some of the notes are represented by an integralnumber of vibrations per second and the number of indicia marks placedaround the periphery of the drum corresponding to these notes will be aneven number and will be equally laid out completely around the drum.

Since the 12 tones of the octave of the chromatic tempered scale areseparated from one another by the ratio of the 12th root of 2, or by afactor of 1.05946, the pitches of A, F-sharp and G will be 220, 370 and392 vibrations per second respectively and integral multiples thereofdepending upon the octaves in which they appear. The remainder of thechromatic scale notes will have a fracn; all

tional number of vibrations per second. With a cylinder rotating at onerevolution per second it is a relatively simple matter to divide theperiphery of the cylinder into an integral number of parts so that asthe cylinder is rotated at one revolution per second and is illuminatedby the neon tube 40, at the corresponding number of vibrations persecond, the eye will view the indicia representing this note as astationary set of indicia marks due to the stroboscopic efiect. Withrespect to the indicia marks corresponding to notes having a nonintegralnum' ber of vibrations per second, I provide a space equal in length tothis fraction of vibration between two of the marks so that the indiciamarks may be placed in a single straight line lying in a plane normal tothe axis of rotation of the cylinder. This results in a slight shif ingof the location which the indicia marks take in each complete revolutionof the cylinder; however, this apparent shifting is small and the linesor indicia continue to remain, during substantially the entire rotationof the cylinder, in a fixed position and the slightly different positionof the marks each revolution is not objectionable to the piano tuner andpermits the single straight line arrangement.

As shown best in Fig. 11, the indicia marks are of wedgeshaped formationand arranged in two groups portions of which are offset with respect toeach other and other portions of which are aligned. When the note beingplayed is of a frequency equal to, or a submultiple of the number oflarge wedgeshaped marks around the periphery of the disk, the patternappears as shown in Fig. 12. When the number of vibrations per second ofthe note being played is double the number of the large wedgeshapedindicia marks, the pattern visible to the eye will look like the patternshown in Fig. 13. The pattern of the next higher octave will look likethe pattern in Fig. 14. Still higher octave notes produce a patternsimilar to Fig. 14 but with the spacing between the points being lessand less. It may, therefore, be seen that with my particular offsetpattern, the octave of the note being played can easily be distinguishedon the stroboscopic device. With the wedgeshaped pattern a higher andhigher octave note may be distinguished and until the space between thepoints become so small that the spacing is not apparent to the humaneye.

If the device were to be used only with musical instruments tuned to aparticular key such as the key of C, to which most, if not all, pianosare tuned, a single set of identifying indicia A to G-sharp could beinscribed in a suitable manner beneath the rows of indicia 118-140because these sets of indicia 1l8l40 would always represent the samenote. Some instruments, especially wind instruments, such as thesaxophone, are often tuned to the other keys such as, for example, thekey of B-fiat, and when so tuned the corresponding number of vibrationsof the various notes are changed.

For example, in the key of C the frequency of vibration of the scale isA, 220 vibrations per second; A-sharp, 233.08; B, 246.95; and theremainder of the notes in the aforesaid ratio of the 12th root of 2. inthe key of Brian, B would have a vibration frequency of 220 cycles persecond, C a frequency of 233.08, C-sharp a frequen y of 246.95 and so onthrough the remainder of the scale.

In order to provide a simple means for indicatin the correctrelationship between the notes and the indicia with instruments ofvarious keys, i provide a relatively movable indexing members 156, 152shown in detail in Figs. 9 and 10 respectively. The indexing member 15%is rigidly mounted on the panel 26 and is provided with a plurality ofapertures 154, 156, 158, 164i, 16 1-, 2.66, 168, 1'79, 172, 174, 176 andcorresponding in number to the sets of indicia 116i4fi and which '2individually aligned with the rotating mark-s. indexing member 552,suitably carried behind the first dexing member 156, is provided withtwo series of indi marks 177 alternately arranged with respect to eachother.

The so One series goes from C-sharp to F-sharp seventeen notes above andthe other series goes from G to C also seventeen notes higher. Uponmovement of the member 152 relative to the member 150, the groups willbe alternately aligned with and be viewable through the apertures154-178 to indicate which of the rows of indicia 116-140 represent whichof the notes in accordance with the key being used. This arrangementmakes it possible to considerably reduce the length of the movablemember 152. The member 152 also has a row of letters 179 thereon whichregister with an aperture 136 in the member 151 and which are cooperablewith an indexing mark 182 carried by the member for determining therelative positions of the indexing members 159 and 152 so that theproper letters appear through the apertures 154-178 to identify theindicia marks 116-140 in accordance to the desired key.

For example, if the members 150 and 152 are relatively positioned sothat the letter C of the key determining row of letters 1'79 appearsbeneath the indexing mark 182, the letters C, C-sharp, D, D-sharp, E, F,F-sharp, G, G-sharp, A, A-sharp, B and C will appear respectivelythrough the apertures 154-178. If, however, the relative position of themembers 15$ and 152 are changed, such that the B-fiat letter of row 179lies under the indexing mark 182, the device 1 is arranged to tune aninstrument of the key of B-flat and the letters D, D-sharp, E, F,F-sharp, G, G-sharp, A, A-shar-p, B, C, C-sharp, and D will appearthrough the apertures 154-173.

The relatively movable indexing members 150, 152 may be mounted in anydesired manner intermediate the opening 30 through the panel 25 and thecylinder 66 whereby it is in the operators line of vision as theoperator views the rotating disk 66. The member 150 is rigidly mountedto the wall or panel 26 by screws 184 extending through the oppositeends of the aperture 30. The fixed member 150 as shown in Figs. 7 and 9is provided with guide channels 186 in which the relatively movablemember 152 is guided for sliding movement relative to the member 150. Apair of pulleys 188 are mounted for rotation upon stub shafts 1% carriedby the panel 26 and an endless cord 192 extends about the pulleys 188and has a portion attached to a downwardly extending projection 194 ofthe movable member 152. The member 194 extends through an elongated slot1% in the lower guide channel 186. The left hand pulley 188 is journaledfor rotation about the left hand stub shaft which is held rigid by thepanel 26. The right hand pulley is fixedly mounted on the right handstub shaft which is journaled for rotation in the panel 26 and has aportion extending outwardly of the panel 26. A control knob 198 securedto the right hand stub shaft is manually rotatable to rotate the righthand pulley for moving the endless cord 192 and thereby the movablemember 152 to index the member 152 relative to member 1511 in accordancewith the key to which the musical instrument is to be tuned.

As shown, the aperture 180 is elongated. it could, however, be of a sizesimilar to that of the apertures 154-178 so that it is just wide enoughto receive one of the key determining letters. The elongated arrangementmakes it easier to determine which way to move the member 152. Ifdesired, the key determining indicia could be placed below the elongatedaperture on the memher 150 and the indexing mark 182 could be carried bythe movable member 152 and movedalong the elongated aperture 13% toregister with the proper one of the key determining letters. Othermodified arrangements will be apparent from the foregoing examples.

Electrical energy for operating the device 1 is obtained from acommercial electrical source by means of a single cord which, when notin use, may be wrapped around the cord receiving hooks 206 as indicateddiagrammatically by the dot dash lines 202.

in order to provide sharp clear stroboscopic effects of the wedge-shapedindicia which terminate in sharp points, it is desirable that the neontube 4% be made to flash brilliantly for extremely short periods of timeso that the ends of the wedge-shaped indicia will remain sharp and notappear as blurs due to the distance the drum rotates while the neon tube40 is emitting light. To do this, I have developed an extremelyeificient electrical controlling network 36 which is schematically shownin Fig. 15. This network comprises the aforesaid valves 44, 46, 4S and5t) and is controlled by the electrical signal placed between thecontrolling grid g and cathode c of the valve 44. The network 36 issupplied with direct current potential of approximately 300 voltsbetween the positive bus 54 and negative bus 56 by any suitable sourceof direct current supply which may be, for example, alternating currentrectified through a suitable rectifying network including the rectifyingvalve 52. Valves 44 and 46 are connected together by various resistorsand condensers to provide a conventional resistance coupled amplifier ofhigh amplification. Upon excitation of the microphone 62 a sine wavewill be impressed between the grid g and cathode c of valve 44 whichwill be amplified in the valves 44 and 46 and applied between the grid gand cathode c of the valve 48 as a high amplitude sine wave. The valve48 is resistance coupled to the valve 50 and, due to the high amplitudeof the sine wave applied between grid and cathode of the valve 48, itsoutput wave will be of clipped wave shape since the amplitude of thecontrol signal to the valve 48 quickly renders the valve 48 fullyconductive and nonco-nductive. This clipped wave is applied between thegrid g and cathode c of the power controlling pentode valve Sti, whichmay be of the 6K6 type. This valve type provides a substantiallyconstant current flow irrespective of the voltage applied between itsanode and cathode so that the current flow between its anode and cathodein response to the clipped wave shape signal applied thereto will besubstantially square shaped.

The positive bus 54 is connected through a current limiting resistor 210and an inductance 212 to the anode of the valve 5%. The cathode of thevalve 50 is connected through a resistor 214 directly to the negativebus 56. The neon tube 41 has one of its terminals directly connected tothe anode end of the inductance 212 and its other terminal connected tothe negative bus 56 and through a capacitor 216 to the end of theresistor 210 which is connected to the positive bus 54.

Upon conduction of the valve 50, current flows through the resistor 210and the inductance 212 to build up a magnetic flux storage of energy inthe inductance 212. When the valve 50 is rendered nonconductive, thefiow of current to the inductance 212 is terminated and the flux thereintends to collapse inducing a high voltage pulse of short duration whichis applied between the terminals of the neon lamp 40 to cause a highintensity short duration ionization of the neon gas in the tube 41 whichilluminates the rotating cylinder 66 for a very short interval. Thevoltage required to cause ionization of the neon tube 40 issubstantially higher than direct current voltage applied between thebusses 54 and 56 so that the neon lamp 40 will not ionize and cause alight emission except during this short interval in which the rapidcollapse of flux in the inductance 212 causes the high voltage to beapplied between the terminals of the neon light 40. The voltage inducedby the rapidly collapsing flux is greatly in excess of the applieddirect current voltage to the busses 54 and 56 and great enough to causeionization of the neon tube 40 and may well rise to magnitude in excessof 1500 volts.

A more detailed description of the network 36 schematically shown inFig. 15 is believed unnecessary since from the above description ofoperation the relative values of the resistors, capacitors, etc. can bereadily determined in the usual manner by those skilled in theelectronic art. I do recommend, however, that the valve 44 be of the 617type, the valve 46 be of the 6817 type, the valve 48 7 be of the 6SF5type and the valve 50 be of the 6K6 type.

In view of the foregoing description of the elements entering into myimproved stroboscopic device 1, a detailed description of its operationis not believed to be necessary. However, I would like to emphasizecertain features. When it is desired to use the tuning device 1, the topcasing section 2 is removed to expose the apertures 30, 94 and 112 andthe knob 198 is tuned .to adjust the member 152 for the key of the pianoor other instrument to be tuned. If it is a piano the lower casingsection is set on the piano with the aperture 94 unobstructed to permitthe light from the aperture 94 to illuminate the works of the piano. Theconnecting wire is connected to a convenient power receptacle and theswitches controlling the illumination of the lamp and of the stroboscopeare turned on. After a short Warm-up time the valves 44-52 will be inoperating condition and the neon tube 40 will being to flash at a highfrequency due to the energy feed back arrangement in which energyradiated by the neon tube is picked up by the short exposed wire portion60. When the note to be tuned is struck the sound picked up by themicrophone 62 will overcome the feed back energy and the light will beflashed at a frequency which is in direct proportion to the frequency ofthe sound wave reaching the microphone to provide stroboscopic effectson the drum 66. The change between the controlling of the neon light 40by the microphone and by the feed back circuit is practicallyinstantaneous so that as far as the operator is concerned the neon lamp40 is continuously supplying pulses of light and the drum 66 is alwaysbeing illuminated. This considerably reduces the fatigue to the musicaltuners eyes.

The motor 82, controlling rotation of the drum 66, is a constant speedmotor and preferably a synchronous motor and is energized concurrentlywith the network 36 so that the drum 66 will be rotating. If the note isof proper pitch the corresponding indicia marks on the drum 66 willappear stationary while, if it is slightly out of pitch, they willappear to rotate slightly in one direction or the other, the rate ofwhich will depend upon the amount of off-pitch of the note.

In the device 1, the microphone 62 is shown built in, however, I haveprovided a connection 220 by which an external microphone can beconnected to control the network 36. In using such an externalmicrophone its connecting cable should be of the shielded type and theconnection 220 is of the shielded type in which the outer sheath of theshielded cable and the outer exposed parts of the connection 236 aregrounded to prevent energy radiating effects from the neon tube 40 fromsupplying an energizing signal to the network 36.

'w'hile I have shown one single embodiment of my invention it will beapparent to those skilled in the art that many changes may be madetherein and still come within the previews of this invention which areto be determined I only by the permitted scope of the hereinafterappended claims.

What is claimed and is desired to be secured by United States LettersPatent is as follows:

1. In an electrical network for controlling the supply of light to astroboscopic apparatus, a power controlling circuit including anelectric valve having an anode and a cathode and a controllingelectrode, an inductor connected to store and discharge energy as aconsequence of changes in the conductive condition of said valve, 2.light source connected to said inductor to receive energy from saidinductor as a consequence of the discharge of said inductor. acapacitor, said light source being connected to said inductor throughsaid capacitor, and means for controlling the conductive condition ofsaid valve.

2. In an electrical system for controlling the supply of light forstroboscopic purposes, an amplifier network including an electric valvehaving a cathode and a control electrode, a power controlling valve,circuit means connecting said network to said power valve whereby saidpower valve is rendered conductive as a function of the conductingcondition of said amplifier network valve, a reactor associated withsaid power valve and arranged to store and discharge energy as aconsequence of changes in the conductive condition of said power valve,an energy radiating light source connected to receive energy from saidreactor as a consequence of said energy discharge, a control circuit forsaid amplifier network valve and including means responsive to anexternally produced input signal for controlling the conduction of saidamplifier network valve and further including means responsive to theenergy radiated from said radiating light source for controlling theconduction of said amplifier network valve.

3. The combination of claim2 in which said amplifier is of the high gaintype, said radiated energy responsive means is ineffective to controlsaid amplifying network valve when said externally produced signals areabove a predetermined minimum magnitude.

4. In an electrical network for controlling the supply of light to astroboscopic apparatus, a power controlling circuit including anelectron-discharge device having two electrodes, an output circuit forsaid device including said electrodes, a source of energy and aninductor, a light source, a capacitor, and means seriallyinterconnecting said light source, said capacitor and said inductor.

5. In an electrical network for controlling the supply of light to astroboscopic apparatus, a power controlling circuit including anelectron-discharge device having two electrodes, an output circuit forsaid device including said electrodes, a source of energy, a resistorand an inductor, a light source, a capacitor, and means seriallyinterconnecting said light source, said capacitor, said resistor, andsaid inductor.

6. In an electrical network for controlling the supply of light to astroboscopic apparatus, a light source, electron-discharge means forcontrolling said source, and means including said light source forcontrolling said electron-discharge means.

7. In an electrical network for controlling the supply of light to astroboscopic apparatus, a light source, electron-discharge means forcontrolling said source, a source of audio-frequency signals, meanscomprising a microphone responsive to said signals for controlling saidelectron-discharge means, and means including said light source forcontrolling said electron-discharge means.

8. In an electrical network for controlling the supply of light to astroboscopic apparatus, a power controlling circuit including anelectron-discharge device having two electrodes, an output circuit forsaid device including said electrodes, a. source of energy and aninductor, a light source, a capacitor, means serially interconnectingsaid light source, said capacitor and said inductor, a source .ofaudio-frequency signals, means comprising a microphone responsive tosaid signals for controlling said electron-discharge device, and meansincluding said light source for controlling said electron-dischargedevice.

9. In an electrical network for controlling the supply of light to astroboscopic apparatus, a power controlling circuit including anelectron-discharge device having two electrodes, an output circuit forsaid device including said electrodes, a source of energy and aninductor, a light source, and means serially interconnecting said lightsource and said inductor.

10. In an electrical network for controlling the supply of light to astroboscopic apparatus, a power controlling circuit including anelectron-discharge device having two electrodes, an output circuit forsaid device including said electrodes, at source of energy and aninductor, a light source, means serially interconnecting said lightsource and said inductor, and means for periodically abruptly changingthe condition of conductivity of said device.

ll. In anelectricalnetwork for controlling the supply of light to astroboscopic apparatus, a power controlling circuit including anelectron-discharge device having two electrodes, an output circuit forsaid device including said electrodes, a source of energy and aninductor, a light source, means serially interconnecting said lightsource and said inductor, said light source and said device beingconnected in parallel with one another, and means for periodicallyabruptly changing the condition of conductivity of said device.

12. In an apparatus for tuning notes of a musical instru ment, arotatable member having a group of equally spaced indicia marks arrangedto pass a fixed point upon rotation of said member, means for rotatingsaid member at a predetermined speed, said indicia marks being so spacedthat when moved by said rotatable member at said speed said marks ofsaid first group pass said fixed point at an integral multiple of thefrequency of vibration of a note to be tested, said speed being suchthat during one rotation of said member said note to be tested vibratesa fractional number of times, said indicia marks being equally spacedfrom a first point on said member to a second point on said member andunevenly spaced between the first point and said second point tocompensate for the fractional vibration, a light source positioned atsaid fiiged point, means for causing said light source to periodicallyilluminate said rotatable member at a first audio frequency ratecomprising an electrondischarge device, and feedback means includingsaid light source and said electron-discharge means for causing saidlight source to periodically illuminate said rotatable member at adifferent rate than said first rate.

References Cited in the file of this patent UNITED STATES PATENTS1,819,494 Aronoif Aug. 18, 1931 1,857,422 Worrall May 10, 1932 1,864,771Sparkes June 28, 1932 1,977,095 Spielman Oct. 16, 1934 2,014,741 LestiSept. 17, 1935 2,174,176 Journeaux et a1 Sept. 26, 1939 2,449,651Hathaway Sept. 21, 1948 2,521,141 Allan Sept. 5, 1950

